1. Field of the Invention
The present invention relates to an inkjet head, a method of manufacturing the inkjet head, and an inkjet recording apparatus. More particularly, the present invention relates to an inkjet head, a method of manufacturing the inkjet head, and an inkjet recording apparatus in which a portion of a pressure chamber is formed by a vibration plate, and the vibration plate is deformed by displacement of a piezoelectric element provided on the vibration plate, thereby changing the volume of the pressure chamber and hence discharging an ink droplet.
2. Description of the Related Art
Inkjet printers (inkjet recording apparatuses) are known which use a so-called inkjet method, where an image is recorded by discharging and propelling ink (ink droplets) from the nozzles of an inkjet head, and causing same to adhere to recording paper, or the like. There are various ink discharge methods for recording heads (inkjet heads) based on an inkjet method. One known method is a piezoelectric method, where the volume of a pressure chamber is changed by causing a vibration plate forming a portion of the pressure chamber to deform due to deformation of a piezoelectric element (piezoelectric ceramic), ink being introduced into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber being discharged as a droplet from the nozzle when the volume of the pressure chamber is reduced. Another known method is a thermal inkjet method where ink is heated to generate a bubble in the ink, and ink is then discharged by means of the expansive energy created as the bubble grows.
An inkjet head using a piezoelectric element, for example, has a laminated structure comprising piezoelectric elements, a vibration plate, a flow passage plate formed with an ink supply passage and pressure chambers, a nozzle plate formed with ink discharge ports (orifice plates), and the like, mounted on a substrate. The head is manufactured by bonding these respective plates together.
Japanese Patent Application Publication No. 2003-94655 describes a method of manufacturing an inkjet head comprising a laminated plate structure of this kind. If piezoelectric elements are formed by general calcination of a thin film, then warping occurs due to the thermal stress generated during the calcination process. Therefore, in order to suppress warping due to thermal stress, in this method, pressure generating mechanisms consisting of piezoelectric elements for driving a vibration plate are formed by inserting a metal film between at least two piezoelectric layers, performing general calcination of the whole structure, and then removing the unnecessary portion in order to obtain a thin film.
This method of manufacture is as follows. In other words, firstly, a thin metal film is sandwiched between a first, 400 μm-thick, piezoelectric layer formed by layering together ten 40 μm-thick uncalcined green sheets, and a second piezoelectric layer consisting of one 40 μm-thick green sheet. A thin metal film for forming electrodes is applied to the lower side of the second piezoelectric layer, and the composition is then laminated together in a press and calcined to form a unified structure. A thermofoam type sheet is then applied to the structure, and the first piezoelectric layer, which is not required in the pressure generating mechanism, is removed by sand-blasting, using the sandwiched thin metal film as a stopper. In this way, the film thickness of the resulting structure is reduced.
Next, the thin metal film forming the stopper is peeled away, and a thin metal film for creating electrodes is formed by sputtering, or the like, on the upper side of the second piezoelectric layer. In this way, the second piezoelectric layer has thin metal films for forming electrodes on its upper and lower surfaces. This second piezoelectric layer is then divided so as to correspond with the positions of the pressure chambers. The second piezoelectric layer which has been divided according to the positions of the pressure chambers is then placed over a vibration plate incorporated with an ink flow passage plate formed with pressure chambers, and the like, the position of the second piezoelectric layer is aligned with the positions of the pressure chambers, and it is then bonded to the vibration plate. Finally, the thermofoam type sheet is peeled away by applying heat, thereby completing the head.